The invention to which this application relates is to the compression of data and in particular image data.
With the increasing use of mobile devices which may have a limited memory capacity and/or network bandwidth for receiving data, the compression of data is becoming increasingly important so that the same can be transmitted and received in a usable format.
A common way of providing indications or options or other information to a user of a device is to provide graphic symbols in addition to text or alternatively to text. However, the volume of data required for graphics can be extremely large, for example, a bitmap image can consist of many pixels and each pixel has an associated color and in modern applications the colors are typically defined from a palette of roughly 16 million available colors. If a bitmap image is 300 pixels wide and 300 pixels high this means that there are 90,000 pixels, each of which may require up to four bytes of color information which can give an image which has 360,000 bytes or 352 KB in size.
Some prior art which is already known is disclosed in U.S. Pat. Nos. 6,091,850 and 5,625,759 which are largely concerned with solving the problem of optimal palette selection. The compression is a side-effect of this process. They do also specify compression techniques, but both patents attempt to compress a bitmap graphic image by analyzing both the shapes and colors in that image and this is largely true of any graphics compression method. Furthermore both patents suggest ways of improving the compression ratio using techniques such as run-length encoding and observe that small groups of pixels can have their color depth reduced to one or two colors in normal images without the results being too detrimental. The present invention aims to improve on these methods by providing a graphics compression method which, when used, can reduce image sizes by a significant amount.